All publications and patent applications herein are incorporated by reference for all purposes to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed inventions, or that any publication specifically or implicitly referenced is prior art.
The goal of plant breeding is to combine in a single variety or hybrid various desirable traits, or to provide a desirable trait without significant detriment to other important properties. For field crops, desirable traits may include resistance to diseases and insects, tolerance to heat, cold and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, maturity, and plant and ear height is important. Other desirable traits may be those directly or indirectly associated with special nutritional and industrial types of crops. Examples of such specialty varieties or hybrids include those with higher oil content, different oil profiles, greater protein content, better protein quality or higher amylose content. It is also desirable to produce plants which are particularly adapted to a given agricultural region. New hybrids are an important part of efforts to control raw material costs.
Maize (Zea mays L.) is often referred to as corn in the United States, and the terms are used interchangeably in the present application. Maize has separate male and female flowers on the same plant, located on the tassel and the ear, respectively. Thus, it can be bred by crossing to itself (self-pollination or selfing), to another plant of the same family, line or variety (sib-pollination or sib-crossing) or to another plant of a different family, line or variety (outcrossing or cross-pollination).
Objectives of commercial maize hybrid line development include the development of new corn hybrids which are able to produce high yield of grain, which require less investment of time or resources, which are more resistant to environmental stresses (e.g., stresses particular to a certain growing area), which are easier to harvest and/or which provide grain or other products particularly suitable for a desired commercial purpose. To obtain a new hybrid, the corn breeder selects and develops superior inbred parental lines for producing hybrids. This is far from straightforward in view of the number of segregating genes and in view of the fact that the breeder often does not know the desired parental genotype in detail. Then, the breeder must identify the particular cross-combination of inbred lines which produces a desired hybrid. Even having obtained two superior inbred lines, there is no guarantee that the combination of these will produce desirable hybrid F1 plants. This is particularly the case because many selectable traits (e.g., yield) are dependent on the effects of numerous genes interacting with each other. Thus, the selection or combination of two parent lines produces a unique hybrid which differs from that obtained when either of the parents is crossed with a different inbred parent line.